The molecular basis for the aciduric properties of Streptococcus mutans will be investigated in this proposal. Utilizing both biochemical and molecular genetic approaches, several of the genes which have been implicated in this environmental response will be investigated. One of these genes recently isolated in this laboratory, dgk coding for diacylglycerol kinase, will be further characterized following purification of its gene product. In addition, since the accumulation of diacylglycerol may mediate external environmental responses in these organisms as has been demonstrated for eucaryotic cells, potential target sites for this cell regulator will be evaluated. Likewise the molecular basis for external acid regulation of diacylglycerol levels will be investigated. Another gene which may play a role in environmental regulation of S. mutans growth, sgp coding for a GTP-binding protein, has been identified immediately downstream from dgk gene within the same operon. Therefore, the role of this gene in environmental stress responses will also be evaluated in this proposal. Furthermore, target sites for the SGP protein will be determined as well as the mechanisms operating to regulate the expression of DGK and SGP. This information will be utilized to evaluate a signal transduction model for the involvement of diacylglycerol and the S. mutans G-protein in aciduricity. Since aciduricity appears to be a key cariogenic property of the mutans streptococci, the information derived from this proposal could be useful in developing novel strategies for neutralizing the cariogenic potential of these organisms.